This statement is backed up by an immense collection of climate science and research, including the most recent report of the Intergovernmental Panel on Climate Change (IPCC), which concludes that a warming climate is “unequivocal.” The IPCC also concludes that global warming is caused largely by human activity, primarily fossil-fuel combustion, and that rising greenhouse gas concentrations will contribute to sea level rise, ocean acidification, and greater risks of droughts, floods, wildfires, and species extinction.

According to recent poll results, the majority of Americans (65%) agree that global warming is caused by humans and an even higher number (81%) see it as a serious problem. Still, there is not much appetite for addressing the implications of this, including in Congress, and it’s vital for the president to continue making this point.

2. “If extracted safely, [natural gas] is the bridge fuel that can power our economy with less of the carbon pollution that causes climate change.”

There’s no doubt that the shift by some electricity generators from coal to natural gas has helped reduce U.S. carbon dioxide emissions. And there are opportunities in buildings, manufacturing and transportation where expanded natural gas use could help reduce emissions in the near and medium term.

But that won’t be enough to get to the significant reductions in emissions we need. To reach our longer term goals, we have to develop more zero-carbon energy sources such as wind, solar and nuclear, and promote energy efficiency and carbon capture-and-storage technologies. We also must remember that methane, the main component of natural gas, is itself a potent greenhouse gas and it’s essential to minimize direct releases of methane into the atmosphere.

U.S. energy-related carbon emissions are 10 percent below 2005 levels, but they crept up 2 percent last year. That's the first annual increase in three years. The Energy Information Administration says it's due to increased electricity demand and also because higher natural gas prices prompted some generators to increase coal use. That's more evidence that market forces alone can't be counted on to reduce emissions sufficiently as long as the cost of emitting CO2 is left out of the market.

3. “The shift to a cleaner energy economy won’t happen overnight, and it will require tough choices along the way.”

In announcing his Climate Action Plan last June, the president articulated a credible and comprehensive process for continuing the nation’s shift to a cleaner energy economy. Of the nearly 50 action items of the plan, the Environmental Protection Agency’s (EPA) carbon emission standards for power plants are receiving the most attention, since they will likely be the most important federal climate action of the next few years. The climate change impact of these rules will be significant: Electric power generation is the largest source of U.S. emissions of carbon dioxide, accounting for roughly one-third of U.S. greenhouse gas emissions. The economic impact of these rules will likewise be significant: More than $100 billion is expected to be spent on new power plant capacity in the next 15 years alone. Together, these environmental and economic impacts will make this among the most important rulemakings in EPA’s history. Balancing the need for steep reductions in CO2 with the need to maintain affordable and reliable electricity will be no easy task.

Add to this the dozens of other action items – which include establishing the next round of fuel economy and emission standards for medium and heavy-duty vehicles, improving appliance efficiency standards, preserving the role of forests in mitigating climate change, supporting local communities as they prepare for climate change, and expanding bilateral engagement with the other major economies – each with its own set of tough choices.

Finally, this: The action plan only goes to 2020, and the administration has agreed to describe next year the measures the U.S. will be prepared to take, in concert with the world’s other major economies, in addressing climate change after 2020.

As the president said, this won’t happen overnight. It’s a good thing we’ve finally started.